Method of sound transducer construction

ABSTRACT

A method of constructing a sound transducer which obviates the need for certain centering and fixture practices relative to assembly of the diaphragm element and voice coil within the air gap defined by a magnet structure. The method consists of forming a rearward or forward oriented frame assembly with selected concentric configurations matingly adapted to receive similarly shaped diaphragm elements and the outer concentric edge of the magnet such that it must then follow that the voice coil is properly positioned within the air gap in non-interfering disposition.

United States Patent 1191 1111 3,792,526

Bremseth 1 Feb. 19, 1974 [54] METHOD OF SOUND TRANSDUCER 3,230,319l/l966 Kliewar 179 1155 R CONSTRUCTION 3,586,792 6/1971 Gayford....29/594 X 1,964,606 6/1934 Thuras l79/ll5.5 R 1 lnvemori Gerald Bremseth,Oklahoma 3,617,654 11 1971 Heidrich 179 1155 R City, Okla. [73]Assignee: LTV Ling Altec, lnc., Oklahoma Primary Examiner Charles W.Lanham City, Okla. Assistant Examiner-Carl E. Hall [22] Filed: Apr. 211971 211 Appl. No.: 135,886 [57] ABSTRACT A method of constructing asound transducer which obviates the need for certain centering andfixture [52] Cl practices relative to assembly of the diaphragm cle- 1Int Cl no 13/00 ment and voice coil within the air gap defined by aFieid 4 602 magnet structure. The method consists of forming a I[79/1155 PC 1155 R 181 R rearward or forvvard oriented frame assemblywith se I lected concentric configurations matingly adapted to receivesimilarly shaped diaphragm elements and the [56] References Cited outerconcentric edge of the magnet such that it must UNITED STATES PATENTSthen follow that the voice coil is properly positioned 2,371,820 3/1945Gustafson 29/594 X within the air gap in non-interfering disposition.3,079,472 2/1963 Sariti 4 3,430,007 2/1969 Thielen 179/115.5 R 4 Claims,6 Drawing Figures i 5? g2 5- 2'4 54 26- 8a m as BACKGROUND OF THEINVENTION 1. Field of the Invention The invention relates generally toacoustic energy transducers and, more particularly, but not by way oflimitation, it relates to improved construction and assembly methods foracoustic pressure transducers.

2. Description of the Prior Art 7 The prior art has relied upon variousmethods for aligning the elements during assembly of loudspeakers andthe like. In assembly, it is mandatory that both the magnet structureand the diaphragm with an attached voice coil must be precisely centeredin an associated frame structure which provides operative support forthe interactive elements. In addition to the centering, the diaphragmmust be held in place in such a manner as to allow a portion of thediaphragm to move or vibrate along the axis of the loudspeaker. In manyprevious methods it was usual to clamp the diaphragm between twosurfaces around a particular circumference referred to as the clampcircumference. It was necessary to key the diaphragm element for usewith a matched magnet and frame structure in order that accuratepositioning of the voice coil with the air gap would be assured. Inother cases, it was necessary to employ tediousfixturing in the assemblyprocess to insure proper insertion of the voice coil in the air gap, andsuch procedures were subject to many forms of assemblers error,carelessness and such; and this often resulted in a high percentage offailures in production.

:SUMMARY OF THE INVENTION The present invention contemplates animprovement in a method of assembly of acoustic energy transducers ofthe type utilizing an electro-magnetically driven diaphragm element. Ina more limited aspect, the invention consists of a method of forming adiaphragm element with a series of concentric, conformativeconfigurations which are identical with concentric, seatingconfigurations and transverse frame element; which transverse frameelement serves to effect proper positioning of both the diaphragmelement and the associated voice coil and magnetic element of theassembly. All elements of critical tolerance as to concentricity andalignment are maintained in proper relationship to enable easy andprecise assembly without the necessity for matching of elements orcomponents.

Therefore, it is an object of the present invention to provide a novelsound transducer wherein the diaphragm is formed with a step structurefor the purpose of centering and clamping. the diaphragm in anassociated frame structure.

It is also an object of the invention to provide a method forconstruction of a loudspeaker diaphragm which may be centered andclamped in an associated frame structure by simple hand assembly withoutthe use of fixturing, cements or secondary operations.

It is still further an object of the invention to provide a method oftransducer assembly which results in considerable cost savings inmanufacture and assembly with a resulting increased functionalperformance.

Finally, it is an object of the present invention to providea method ofsound transducer assembly which insures proper interactive positioningof the several component elements of the transducer, and which enables amore reliable assembly procedure with reduction of assembly failures.

Other objects and advantages of the invention will be evident from thefollowing detailed description when read in. conjunction with theaccompanying drawing which illustrates the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation of a soundtransducer in partial section as constructed in accordance with thepresent invention;

FIG. 2 is a front elevation of a transverse frame element constructed inaccordance with the present invention;

FIG. 3 is a front elevation of a diaphragm element constructed inaccordance with the present invention;

FIG. 4 is an exploded side view in vertical section showing a magnetassembly, diaphragm and transverse frame element; I

FIG. 5 is a side elevation of a reverse oriented sound transducer inpartial section which constitutes an alternative form of the invention;and

FIG. 6 is an exploded view in vertical section of still another form ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION Referring now to FIG. 1, an energytransfer portion of a sound transducer 10 e.g. a horn loudspeakerassembly, is shown as consisting of a horn element 12 formed integrallyas by molding with a main frame 14, and having the anterior or rearp'a'rt closed over by a rear frame 16, shown in dash-lines. A foldedsound energy director element 17 is connected to the main frame centeralong the axis thereof. The rear frame 16 may define a chamber or space18 of predetermined volume wherein weather proof connection terminals,control relays or such may be located.

The transducer 10 includes'driving structure consisting of a magnetassembly 20 secured in coactive relationship with a diaphragm elernent22supporting the voice coil 24, and a transverse frame 26 provides seatingand centering support as it is assembled in contact with both thediaphragm element 22 and magnet structure 20. See also FIGS. 2, 3 and 4which show the essential elements of the driver in greater detail. Theopposite side of frame 26 is formed to receive main frame 14 anddirector element 17 in-operative engagement.

The magnet assembly 20 is of a conventional formation wherein poleelements are formed by a rear ring 28, forward ring 30 and center ring32 assembled as shown for coaction with a ring-shaped magnet 34, e.g. aceramic magnet composition or the like. The forward ring 30 is securedin concentric relationship with respect to the center ring 32 to definean air gap 36 extending axially of magnet assembly 20. A central bore 38is formed through the center of the center pole piece 32 and front polepiece 28 to allow passage of vibratory energy in alternative structures,as will be further described. I

The diaphragm element 22 is formed as a unitary transverse structure 40as formed from conventional substances such as phenolic compositions,impregnated linens and the like, and a coil former 42 carrying voicecoil 24 is secured as by cementing to the rearward part of the diaphragmelement 22, as will be further described below. A pair of energizingleads 44 and 46 may be lead through respective holes 48 and 50 inelement 22 for conductive connection to the voice coil 24.

Actually, the voice coil 24 may be wound on coil former 42 withallowance of additional conductor material to be lead out as energizingleads 44 and 46.

The element 22 is formed with an outer annular ring 52 which serves as aclamping surface in the assembled structure. The outer annular ring 52then extends into forwardly extending cylindrical portion 54 whichextends axially of the loudspeaker assembly into further formation of asecond annular ring 56. In like manner, the inner edge of second annularportion 56 extends into a second cylindrical portion 58 proceedingforwardly along the axis of the loudspeaker l0, and the center portionof element 22 is filled out as the vibratile or sound-moving portion 60.A stiffening ring 62 is formed on vibratile portion 60 at about theinner diameter of center pole piece 32 to damp out adverse vibrations.The coil former 42 is then secured as by cementing around the innersurface of the second cylindrical portion 58 of diaphragm element 40,this rendering the voice coil 24 at a precise concentric positioningrelative to the second cylindrical portion 58, and the first cylindricalportion 48, as well as the precisely formed annular portions 56 and 52and the outer perimeter of diaphragm element 22.

Referring now more particularly to the transverse frame 26, the variousmating and centering facilities of this element are formed to be ofprecise nature relative to the similar concentric configurations ofdiaphragm element 22. Thus, the transverse frame 26 is unitarily formedbut including various step portions for enabling mating and centeringfunctions. The transverse frame 26 is molded or otherwise formed toinclude a series of concentrically arranged bores which define aplurality of annular shoulder portions and cylindrical inner walls ofcritical dimension. An outer flange 64 is formed to include a pair ofguide holes 66 and 68 which may be utilized in the initial lining up aswell as for fastening in the assembly process. The inner edge of outerflange portion 64 is then formed to define a cylindrical wall 70 whichterminates in an annular shoulder 72 which, in turn, is formed to definea cylindrical wall 74 terminating in an annular shoulder portion 76. Theannular portion 76 again forms a cylindrical wall 78 which tenninates ina base portion 80 to complete the transverse frame 26. The base portion80 includes axially open portions 82 to allow passage of air. A pair ofoppositely disposed holes 84 and 86 are formed to receive the energizingleads 44 and 46 therethrough, and channel formations 88 are formed toallow interference free lead out of the energizing leads.

The method of the present invention enables a selfcentering feature dueto the fact that the diaphragm element 22 is formed with steps orcylindrical portions 54 and 58 formed as an integral part thereof, andbeing precisely formed so that the proper mating within the bores orcylindrical side walls 74 and 78 will assure proper centering of thediaphragm element 22 without the necessity of using fixtures, cement orother securing agents. The outer annular portion 52 of diaphragm element22 seats against the shelter or annular surface 72 of transverse frame26 and, upon'proper assembly, the forward ring 30 of magnet assemblyfits securely within cylindrical wall 70 of transverse frame 26 such hatit serves to clamp the diaphragm annular portion 40 securely about itsouter periphery, as well as to provide proper alignment as between airgap 36 and coil former 42 and voice coil 24. Proper keeping oftolerances in forming of parts, as between the inner and outer diametersor edges of forward ring 30 and the mating portions of diaphragm element22 and transverse frame 26, will always assure that voice coil 24 rideswithin air gap 36 in non-interfering relationship to provide dependableoperation at maximum efficiency.

It is also contemplated that the diaphragm may be constructed to providea reliable, accurate clamp circumference which provides the clearancenecessary for movement or electrical connections without the use ofgaskets or shaped clamping structure. Such alteration would be a designconsideration and well available within normal skill.

The self-centering diaphragm element 22 offers sev eral advantages overconventional methods. Thus, it not only enables centering of the voicecoil 24 in the air gap 36, but it assures non-interfering freedom ofmovement therein. This non-interfering insertion is accomplished with aminimum of air gap which results in a net gain in efficiency of theloudspeaker.

The structure of FIG. 5 illustrates an alternative form of soundtransducer wherein the sound producing assembly is oriented oppositefrom that of the FIG. 1 structure Thus, a transducer 90 consists of ahorn portion 92 defining sound throat 94 and including integrally formedfront frame portion 96 for coaction with a transverse frame 98. Thetransverse frame 98 is precisely formed with mating configurations aswill be further described, to secure a diaphragm 100 and associatedvoice coil 102 in proper mating interaction with magnet assembly 104which defines an air gap 106.

In this alternative form, the transverse frame 98 includes a pluralityof concentric, cylindrical bores 108 and 109 spaced by annular portion110 which coact with precise, form-fitting configurations on diaphragm100 to ensure proper centering of voice coil 102 within air gap 106. Thetransverse frame 98 is essentially the same as transverse frame 26 ofFIGS. 1, 2 and 4 except that it is formed for opposite orientationrelative to the sound producing and directing assemblies. Thus,transverse frame 98 includes a raised central portion 112 which forms aconcave and centrally aligned structure relative to the diaphragmelement 100.

The diaphragm element 100 is also precisely formed for mating engagementwithin transverse frame 98 thereby to assure proper alignment of voicecoil 102. The diaphragm element 100 includes an outer annular portion114 formed integrally with a firstv cylindrical portion 116 and secondannular portion 118 for mating engagement within the counterpartportions of transverse frame 98. A second or inner cylindrical portion120 recieves coil former 122 therewithin in what is a properly fixturedposition relative to the functional interaction of components of thesound transducer 90.

The magnet assembly 104 is essentially the same as the magnet assembly20 of the FIG. 1 embodiment except that it functions in a differentmanner to receive acoustic pressure or sound energy through its axialcenter for progression out through the throat 94 of horn 92. Thetransverse frame 98 is also formed to have an annular portion 124connecting inner cylindrical bore 109 and the center portion 112, theannular portion 124 being aligned at a rearward angle slightly displacedfrom the transverse axis such that the central portion 112 forms an airspace 126 in between diaphragm element 100 and transverse frame 98thereby to allow space for vibratile movement of the diaphragm element.

FIG. 6 illustrates still another embodiment wherein a magnet-diaphragmassembly is formed for precise, mating engagement. Thus, amagnet-diaphragm assembly 130 consists of a magnet assembly 132, whichis formed essentially as the aforementioned magnet assemblies and 104.Magnet assembly 132 includes an annular groove 134 formed concentricallywithin the rear face 136 of a pole element ring 138. A diaphragm element140 is then precisely formed to include an annular shoulder or ringportion 142 formed integrally about front face of an outer annularportion 144 of diaphragm element 140. The ring portion 142 is formed inprecise manner to mesh with the annular groove 134 in mating engagement,and when such engagement is effected a voice coil 136 is assured ofproper noninterfering-fit within air gap 148 of magnet assembly 132. Thediaphragm element 140 further includes a concentric cylindrical poriton150 which defines a surface for receiving coil former 152 in properlyaligned relationship, and the central part of the diaphragm element 140is then completed as a dome portion 154 which provides the actual airmoving medium. A clamping ring 156 of conventional type may then beutilized to secure the diaphragm element 140 in properly positionedmanner against the rear side of magnet assembly 132, ring portion 142being matingly received within groove 134.

' The previous discussion describes those cases where both the diaphragmand themagnet assembly are centered in a separate transverseframeyhowever, the novelty advanced herein will also apply in thosecases where the diaphragm element is centered by utilizing the magnetstructure itself. An example of such diaphragm centering is that whichmust be effected relative to dome radiator loudspeaker assemblies ofrecently evolved type. Such loudspeakers are extremely simple in conceptand design but proper centering of the diaphragm element is verydifficult to achieve. The fixturing of such dome elements is extremelydifficult such that many manufacturers resort to blind assembly, orassembly by feel, and this results in a very high reject rates.Requisite provisions of large air gap necessitated by assembly techniquetends to decrease efficiency. These problems are overcomeutilizing thekey-formed diaphragm and frame structures as described herein, at thesame time effecting minimum air gap and maximum efficiency, i.e.efficiency varies inversely with the volume of the air gap.

The present invention would apply to all transducers using a diaphragmin conjunction with an electrical voice coil operating in an air gap;viz., cone loudspeakers, horn driving units, dome or diaphragmloudspeakers, diaphragm microphones, under water loudspeakers ortransducers, etc. The method of construction offers a solution to somemajor problems in construction of such units and it is considered to bedistinct improvement in transducer fabrication and assembly. Theselfcentering diaphragm eliminates any fixturing operations, and allcritical dimensions are part of the molding or forming tool itself whichcan be precisely maintained for all components of a plurality ofassemblies Without need for component matching. Thus, the self-centeringdiaphragm is not only a separate concept but it also provides a moreaccurate method of assembly.

Changes may be made in the combination and arrangement of steps and/orelements as heretofore set forth in the specification and shown in thedrawing; it being understood that changes may be made in the embodimentsdisclosed without departing from the spirit and scope of the inventionas defined in the following claims.

What is claimed is:

i 1. A method of constructing a sound transducer of the type whichincludes a transverse frame element securing a permanent magnet assemblydefining an air gap, a diaphragm element and a voice coil in properoperative position, such construction comprising the steps of:

forming said diaphragm element unitarily to include at least oneconcentric surface around an outer portion of said diaphragm element,which concentric surface extends parallel to the axis of movement of thediaphragm element, said diaphragm element further supporting aconcentric voice coil in secure affixure;

forming said magnet assembly to define an air gap for non-interferingcoaction with said voice coil when assembled, said magnet assembly beingformed to have a selected diameter of that portion adjacent thediaphragm when assembled;

forming said transverse frame element to include a first cylindricalbore having said pre-selected diameter, and a second cylindrical boretherein which is concentric but having a reduced diameter such that thesecond cylindrical bore wall will receive said diaphragm elementconcentric surface securely therein; and

assembling the diaphragm element, magnet assembly and transverse frameelement to form the sound transducer wherein the cylindrical surface,cylindrical bores and magnet assembly of pre-selected diameter cooperateto orient and position the diaphragm element and voice coil, thetransverse frame, and the magnet and air gap in proper operativeposition. Y

2. A method of constructing a sound transducer as set forth in claim 1wherein said step of forming said diaphragm element further comprises:

forming a first annular portion having concentric inner and'outer edgesto extend outward from and adjacent to the forward edge of said at leastone concentric surface, and a second annular portion having concentricinner and outer edges to extend inward from and adjacent to the rearedge of said at least one concentric surface to further form a

1. A method of constructing a sound transducer of the type whichincludes a transverse frame element securing a permanent magnet assemblydefining an air gap, a diaphragm element and a voice coil in properoperative position, such construction comprising the steps of: formingsaid diaphragm element unitarily to include at least one concentricsurface around an outer portion of said diaphragm element, whichconcentric surface extends parallel to the axis of movement of thediaphragm element, said diaphragm element further supporting aconcentric voice coil in secure affixure; forming said magnet assemblyto define an air gap for noninterfering coaction with said voice coilwhen assembled, said magnet assembly being formed to have a selecteddiameter of that portion adjacent the diaphragm when assembled; formingsaid transverse frame element to include a first cylindrical bore havingsaid pre-selected diameter, and a second cylindrical bore therein whichis concentric but having a reduced diameter such that the secondcylindrical bore wall will receive said diaphragm element concentricsurface securely therein; and assembling the diaphragm element, magnetassembly and transverse frame element to form the sound transducerwherein the cylindrical surface, cylindrical bores and magnet assemblyof pre-selected diameter cooperate to orient and position the diaphragmelement and voice coil, the transverse framE, and the magnet and air gapin proper operative position.
 2. A method of constructing a soundtransducer as set forth in claim 1 wherein said step of forming saiddiaphragm element further comprises: forming a first annular portionhaving concentric inner and outer edges to extend outward from andadjacent to the forward edge of said at least one concentric surface,and a second annular portion having concentric inner and outer edges toextend inward from and adjacent to the rear edge of said at least oneconcentric surface to further form a central vibratable portion.
 3. Amethod as set forth in claim 2 wherein said central vibratable portionis formed to include a second concentric, cylindrical surface equispacedwithin said first concentric surface to receive the voice coil securelyin axial alignment therewith.
 4. A method as set forth in claim 3wherein said step of forming said frame element comprises: furtherforming said frame element to include similar mating shapes to receiveeach of said diaphragm element first and second annular portions andfirst and second concentric surfaces in secure juxtaposition.